In arthroplasty, a bone is altered to subsequently receive thereon an implant. For example, in hip arthroplasty, the acetabular cup implant is received in the reamed acetabulum and serves as a receptacle for a femoral head or femoral head implant. Accordingly, tools such as a reamer and a cup impactor are used in the procedure.
One of the challenges in such procedures is to provide an adequate orientation to the tool or implant relative to the bone. An inaccurate orientation, for instance in the case of an acetabular cup implant, may result in a loss of movements, improper gait, and/or premature wear of implant components. For example, the acetabular cup is typically positioned in the reamed acetabulum by way of an impactor. The impactor has a stem at an end of which is the acetabular cup. The stem is handled by an operator that impacts the free end so as to drive the acetabular cup into the acetabulum. It is however important that the operator holds the stem of the impactor in a precise three-dimensional orientation so as to ensure the adequate orientation of the acetabular cup, in terms of inclination and anteversion. Accordingly, the knowledge of the initial position and orientation of the bone relative to an inertial sensor unit can contribute to subsequent steps of altering the bone and positioning an implant thereon.
Computer-assisted surgery has been developed in order to help operators in positioning and orienting implants to a desired orientation. Among the various tracking technologies used in computer-assisted surgery, optical navigation, C-arm validation and manual reference guides have been used. The optical navigation requires the use of a navigation system, which adds operative time. Moreover, it is bound to line-of-sight constraints which hamper the normal surgical flow. C-arm validation requires the use of bulky equipment and the validation is not cost-effective, yet does not provide a quantitative assessment of the cup positioning once done, and is generally used post-operatively as opposed to intra-operatively. Finally, manual jigs, such as an A-frame, do not account for the position of the patient on the operative table. Accordingly, inertial sensors are used for their cost-effectiveness and the valuable information they provide.